THESOLID PHASEIN
Feb., 1934
THE
small temperature coefficient, contrary to the experimental findings of this investigation. He will also show in a forthcoming publication that the addition of Br3 to a double bond requires an energy of activation greater by 10,000 calories than that required for the addition of Br2. Making the reasonable assumption that the calculations can be applied to cinnamic acid in carbon tetrachloride solution, i t is apparent that Purkayastha and Ghosh’s chain fails to explain the observed facts because i t includes a step which is slower even than the thermal bromination in the dark. Further experiments are in progress, designed to test the relative merits of the hypotheses of energy and chemical chains.
Summary 1. The photobromination of cinnamic acid in carbon tetrachloride has been measured quantitatively with a monochromator. The influence
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of concentration, temperature and wave length on the quantum yield has been studied. 2. The reaction is a chain reaction. The quantum yield, a, ranged from 1 to 15 or more, depending on the concentration of the bromine and the temperature. The reaction was studied over a range of from 2 X low3 to S X mole of bromine per liter, and a t temperatures of 0, 10, 20 and 30’. 3. The photochemical reaction has been shown to consist of two parts; first, a primary photo reaction of one molecule per quantum, and, second, a photo-excited thermal reaction which is measured by a- 1, or 8, and which is suppressed a t great dilution of bromine or a t low temperatures. Log 8 plotted against 1/T gives nearly straight lines whereas log @ plotted against 1/T does not. 4. The experimental facts are in agreement with a theory involving activated bromine molecules and an energy chain. MADISON, WIS.
RECEIVED NOVEMBER 3, 19333
CHEMICAL LABORATORY OF ~VASHINGTON SQUARE COLLEGE, NEWYORKUNIVERSITY 1
The Nature of the Solid Phase in the System Antimony-Bismuth1 BY W. F. EHRETAND 31. B. ABRAMSOK Although a number of investigations have been made of the antimony-bismuth system, employing practically all of the usual physical methods, there has been no general accord on the nature of the solid phase nor on the position of the solidus in the equilibrium diagram. Studies by Hiittner and Tammann,2 G a ~ t i e r Sapossni,~ koff ,* and Parravano and Viviani5 indicated that the solidus corresponded to an isomorphous series of alloys, the curve dropping sharply from the melting point of antimony to 269” a t a composition of io% antimony and continuing horizontally from that point to the melting point of pure bismuth. Cook,6from a careful thermal investigation, obtained the solidus shown in Fig. 1. &ani7 more recently studied the equilibrium ( l J Presented in part before the Physical a n d Inorganic Division a t t h e 86th meeting of the American Chemical Society, Chicago, Illinois, September 11-15, 1933. (2) Huttner and Tammann, Z . anorg Chem., 44, 131 (1905). (3) Gautier, “Contribution h I’htude des alliages,” Paris. 1901, p. 114.
(4) (5) (6) (7)
Sapossnikoff, J. Russ. Phys.-Chem. Soc., 40, 665 (1908). Parravano and Viviani, Rend. accad. Lincei, 19, 835 (1910). Cook, J. Insl. .uc/als, as, 421 (1922). &ani. S r i . K e p / s . TBhoku I m p . Uniu., 13, 293 (1924-5).
diagram by the electrical resistance method. His solidus did not show the horizontal portion but gave the normal curve for a complete series of solid solutions (Fig. 1). After the present investigation had begun, an x-ray analysis of antimony-bismuth alloys was published by Bowen and Morris Jones.* They concluded that the lattice parameter varied almost linearly with the weight per cent. of the components, a slight curvature being noticed a t the antimony end. There was no evidence of intermetallic phases other than the solid solution. From purely thermodynamic considerations, Yap9 explained the horizontal solidus by assuming a peritectic reaction between a solid solution a[Sbz-Biz] and the melt, forming solid solution /3[Sb2-Bia]. In this event there should be two solid solutions present between the limits of 33 and (io mole per cent. bismuth (Fig. 1). The present x-ray investigation was undertaken to see whether any such solutions existed. (8) Bowen and Morris Jones, P h i l . Mar., 171 13, 1029 (1932). (9) Yap, Tech. Publication 397, Trans. A m . Insl. Mining M e t . I:ng , Inst. Metals Division (1931) T h e authors wish t o thank hIr Y a p , Chu-fhay for his interest and aid in t h e present work.
386
W. F. EHRETAND M. B. ABRAMSON
Experimental Alloys for the investigation were prepared from Kahlbaum antimony and bismuth using the usual vacuum technique. Samples 5-12 (Table I) whose melting points fall on the horizontal portion of Cook’s solidus were annealed simultaneously. The furnace was kept a t 300” for a short while and then lowered to 280 * 3.0”, a t which temperature i t was maintained for 230 hours, then slowly brought to room temperature over an interval of 150 hours. All other samples were treated similarly, starting the annealing above the melting point in each case. I n most instances microscopic examination revealed large,
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constant, 2.814 A,), was recorded a t the same time and upon the same photographic film as the pattern for each alloy. x-Ray Data.-Calculations made in the present work were for the lattice values of the small rhombohedron. In the case of bismuth and antimony the axes are mutually inclined a t 57’10’ and 57”5’, respectively.” Since the axial angles of the two metals differ by only ll’, the angles of the intermediate alloys were assumed to vary linearly with the mole per cent. of the components; any possible error in this assumption would result in ail error in the calculations which would fall well within the experimental error. The results of the calI culations are given in Table I and Fig. 2. The accuracy -~ attained in determining the lattice constant is *O.OO; A.
Discussion of Results The diffraction patterns obtained in all cases showed the same series a -S o l i d Solvtion of lines with similar rela3 0 0 b - [Sb,-Bt,! tive intensities, all corresponding exactly with the ; a+B zoo-----[Sb,-B,,] equation for the rhombo1 1 I (Yo P) hedral unit of structure. Sb 20 40 60 80 Bi KO evidence of another Weight percentage of bismuth. pattern or “super-strucFig. 1.-Constitutional diagrams of system Sb-Bi. ture” was found. It is well-defined polygonal grains with no indication of hetero- thus seen, both from the x-ray and microscopic geneous structure. In a few cases a dendritic structure investigation, that alloys of antimony and bismuth was coexistent with the polygonal, indicating that the of all compositions, when properly annealed above process of transition t o the latter form had not been comthe melting point, consist of an unbroken series of pleted. solid solutions. This is in accord with the results TABLE I of Cook’s and Huttner and Tammann’s analyses Lattice Weight, Mole, constant and is contrary to Guertler’s assumption12 of the Sample % Sb % Sb aa in A. formation of an eutectic and I‘ap’s postulation of 100 Sb 100 4.492 two solid solutions. 1 86.0 91.6 4.519 2 66.1 78.3 4.555 The parameters of the rhombohedra were found 3 68.7 4.577 56.1 to vary linrdrly with the mole per cent. of the 4 52.9 65.9 4.580 components. The value used for pure bismuth 5 51 0 64.1 4.582 was that of Ehret and Fine’? (ao = 4.749 k ) . ti 47.3 60.0 4.592 -I Bowen and Morris Jones found from their x-ray 54.2 40.8 4.607 35.1 48.2 8 4.620 investigation of this system that the lattice 9 41.0 28.8 4,643 varied almost linearly with the percentage by 10 25.0 36.0 4.046 weight of the components, with a slight curvature I1 16.3 25.0 4.713 a t the antimony end. In a solid solution of the 12 6.1 10.0 4.733 substitution type the change in parameter should Bi 4.749 not be determined by the weight of the atoms The powder method and the standard type of General introduced but by the number of such atoms. Electric (Davey)Iodiffraction apparatus was used for the Consequently, when the variation of the parax-ray investigation. For purposes of standardization, _f
-_.I-
I
I
the diffraction pattern of pure sodium chloride (lattice (10) Davey, Gcn. Eiec. Res., 56, 565 (1922).
(11) Neuburger. Z Krtsl , EO, 103 (1931) ( 1 2 ) Chertler “Metallographie ’ Vol I , p 798 (13) I. hret and I me, Phil M u g , [ 7 ] 10, 5 5 1 (1930)
THESOLID
Feb., 1934
PHASE I N THE
meter is plotted against the mole per cent. of the components, the resulting curve can be more accurately interpreted as the true effect on the crystal units produced by alloying the two metals. The value for the edge of the face-centered rhombohedral lattice for bismuth as given by Bowen and Morris Jones (no = 6.540 A.)is lower than previous values, and differs considerably from that accepted by Neuburger'* (a0 = 6.578 A.) jn his critical r6sum6 of lattice constants of the elements. If the values of the intermediate alloys as given by Bowen and Morris Jones are replotted against the molar percentage, and the last mentioned value for bismuth is used, a linear relation is evident simiIar to that found in this investigation
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387
tablish the true solidus using thermal methods will be seen from the following experiment in which the authors attempted to establish the melting point of a 40 weight per cent. Bi alloy. The latter was cooled from the molten state to 400' and kept a t this temperature for 300 hours, after which i t was slowly cooled, over a period of three days, to B O " , a t which temperature (*2') it was annealed for 300 hours. Slow cooling, over a period of ten days, then brought the alloy to room temperature. This procedure had been shown by Cook to be the most rapid way to attain homogeneity, The sample thus obtained was practically homogeneous and consisted of Iarge polygonal grains. When heated a t an
Molecular percentage of bismuth. Fig. 2.-Variation in lattice parameter in Sb-Bi alloys: ordinates at left permit plotting of the edge-length of the unit rhombohedra (present work), small circles; ordinates a t right permit plotting of edge-length of face-centered rhombohedra against molecular per cent. (recalculated from work of Bowen and Morris Jones), small triangles.
(Fig. 2 ) . Because of this simple relationship between lattice dimensions and molecular percentage, the equilibrium diagram of this system when obtained from annealed alloys is believed to be of the normal type as found by &ani. The horizontal solidus obtained by Cook cannot be considered part of the true equilibrium diagram and may be explained, as he suggested, by assuming that there is only a small amount of diffusion in the crystals separating from the melt during the cooling process. If the crystals so obtained are properly annealed, diffusion is increased and equilibrium is attained; the melting points of such annealed alloys will then lie on the normal solidus as obtained by btani. That i t is difficult to es(14) Scuburgrr. Z
Krrcf
80, 103 (1931)
average rate of 1.6' per minute to 465", there were no perceptible halts in the time-heating curve even though the alloy had been partially melted as shown by the microscope. Such behavior can be understood for a solid solution since the melting point rises gradually but it seems to rule out definitely the existence of a compound, eutectic, or peritectic reaction in this alloy.
Summary 1. x-Ray diffraction and microscopic examinations of annealed specimens of antimonybismuth alloys show them to consist of one phase only, corresponding to a system which forms a complete series of solid solutions.
LYLEVERNONANDREWS AND D. J. BROWN
3%
2 . The lattice parameter was found t o vary linearly with the mole per cent. of the components.
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3. &ani’s curve is believed to be the correct equilibrium solidus for this system. NEWYORKCITY
RECEIVED NOVEMBER 4, 1933
CHEMICAL LABORATORY, UNIVERSITY OF SBBRASKA j
The Potentials of the Lead Oxide Electrodes in Alkaline Solution’ BY LYLEVERNON ANDREWS AND D. J. BROWK Glasstone,2 who measured the lead oxide-lead normal potassium hydroxide solution. The soludioxide electrode, worked with normal solutions tion from which the lead dioxide was deposited, of sodium hydroxide only. Since lead oxide acts contained about 0.570 of lead nitrate and was as an acidic oxide in concentrated alkaline solu- about 2 normal in nitric acid. A current density tion, the activity of the sodium hydroxide in the of approximately 0.003 amp./ sq. cm. was used.: Lead orthoplumbate was prepared by treating two half cells would be different. It has been shown by Glasstone2 and iMilbauer3 that lead lead dioxide, deposited on platinum foil, with a dioxide in contact with an alkaline solution of solution 0.3-1 .O normal in potassium hydroxide lead oxide reacts t o form the oxide commonly and almost saturated with lead oxide, for ten to called red lead, Pb304 which has also been shown fifteen hours at about SO‘. These conditions by Glasstone to be lead orthoplumbate, PbzPb04. have been shown by Glasstone2 and Milbauer3 In view of these facts i t would seem impossible to give lead orthoplumbate. The deposit adto obtain a standard potential using lead oxide heres firmly, and forms a coating over the lead and lead dioxide in the alkaline half cell. It dioxide. Lead oxide, red variety, was precipitated from a should, however, be possible to make the measurement in two steps, using lead ofthoplumbate as hot 12 normal solution of potassium hydroxidefi the intermediate product and calculate the oxida- by adding powdered lead acetate to the hot alkali. The oxide was washed by decantation with hot 10 tion potential. For a reference electrode, we decided upon the normal potassium hydroxide, then washed thorHg-HgO(s)-OH- e l e ~ t r o d e . ~The two cells pro- oughly and repeatedly with hot distilled water and dried over sulfuric acid in a vacuum desicposed are cator. Analysis for lead’ gave 99.7% PbO. A H~-H~O(S)-P~O(S)-KOH-P~O(S)-P~~O~(S)-P~ (1) small amount of water was evolved when thc H~-H~O(S)-KOH-P~O~(S)-P~~O~(S)-P~ (2) When an electron current passes through the oxide was heated strongly. Potassium hydroxide solution was prepared as cells from right‘ to left, the following reactions described by Ming Chow.4 Doubly distilled take place water, distilled in an all-Pyrex still, first from H g + PbaOa HgO 4-3 P b 0 alkaline permanganate and then redistilled from 2Hg 3PbOi 2Hg0 Pb304 the clean still, was used to prepare all solutions. These equations indicate that the electromotive Saturated solutions of the oxides were made in force of the cells should be independent of the 200-ml. round-bottomed, long-necked flasks, fitted concentration of the alkali. with ground-glass stoppers and provided with Lead dioxide was deposited on platinum foil, rubber caps to prevent carbon dioxide from workmade rough either by coating with platinum ing past the ground-glass stoppers. These flasks black and then heating in a blast lamp, or by were almost filled with solvent, an excess of the treating the smooth foil with hot aqua regia for a solid oxide added and then shaken in a constant few minutes. The roughened platinum was cleaned with hot concentrated nitric acid, fol- temperature air-bath a t 23.0 * 0.3’.
+
e
+
lowed by a half hour treatment with hot half (1) Original manuscript received January 3, 1933 ( 2 ) Glasstone, J Chem Soc , 121, 1456 (19221, 1469 (1922) (3) hlilhauer, Chem Zezt 38, 587 (1914) ( 4 ) Afing C h o n , ’lHIS
JOURNAL,
42, 488 (1920)
(5) Smith, THISJOURNAL, 27, 1287 (1905): Fischer and Schleicher, “Elektroanalytisch Schnellmethoden,” zweite Auffage, 1926, p. 243. (6) Smith and Woods, ihid , 46, 2632 (1923). ( 7 ) Brown, >loss and R’illiams. I n d . Eng. C h e m . . .\nul. E d . , 3. 134 (1931).
